H heidelbergensis

Figure 1.5 The hominin phylogeny. Lines linking the branches were not included because many of the relationships between the species remain unclear. However, there is good evidence that Ardipithecus (Ar. ramidus kadabba and Ar. ramidus) were ancestral to the australopiths A. anamensis and then A. afarensis in an evolutionary lineage. Prior to that scientists are still investigating Sahelanthropus, Orrorin, and Ardipithecus for evidence of their belonging to either the human or the chimpanzee lineage since they are located so close to the time when the two modern species are estimated (by molecular clocks) to have split about 6 Mya. A. afarensis is normally rooted at the base of both the Paranthropus and the Homo lineages, but sometimes A. africanus is put on the direct line to Homo too. The genus Paranthropus (P. aethiopicus, P. robustus, and P. boisei) is an evolutionary side branch from the direct lineage leading to humans that went extinct around 1 Mya. H. habilis and H. rudolfensis may have just been one highly variable species and A. garhi looks like it was the ancestor to these earliest members of the human genus. Some scientists lump H. ergaster fossils in with H. erectus but some keep itseparate as it is shown here. H. heidelbergensis is an Archaic species that was probably involved in the evolution of Neanderthals (H. neanderthalensis) and modern humans (H. sapiens). H. floresiensis was a small-bodied and small-brained hominin known only so far from the Indonesian island of Flores that overlapped in time and space with modern humans, but may be dwarfed descendents of H. erectus. It will be helpful to refer to this figure as you read the descriptions of the species in Chapter 3. Illustration by Jeff Dixon.

Table 1.2 Current Questions in Human Origins and Evolution

• Is Homo floresiensis a valid species of dwarf hominin or is it diseased?

• Did modern humans around the Old World evolve in place from earlier hominin forms or did they evolve in Africa and spread to other regions, replacing those forms?

• Were Neanderthals directly involved in our own evolution? Did modern humans and Neanderthals interact?

• Why did the Neanderthals go extinct?

• Why did the robust australopiths—the genus Paranthropus—go extinct?

• Would we be able to recognize the earliest fossil hominin if we found it? How would we distinguish it from the earliest fossil chimpanzee?

• Why did bipedalism evolve?

• To what extent did meat-eating shape human evolution and enable brain size to increase?

• When did language evolve?

• Why are some traits, like darkly pigmented skin, more prevalent in some human populations compared to others?

• Is natural selection still affecting human populations? Are humans still evolving?

highlight a few of the popular research topics in the field. Fundamental concepts and evidence used to address these questions are introduced throughout the rest of the book.